The invention relates to an electric motor assembly, particularly for driving a fan for an engine cooling system and/or an air conditioning system of a motor vehicle, comprising an electric motor and a motor control device for activating the electric motor. The invention also comprises a method for operating an electric motor and a motor control device.
Electric motor assemblies of the type stated at the beginning are known. They are often used for driving a fan of a motor vehicle, this fan being assigned for example to the engine cooling system and/or the air conditioning system. To set the power of the fan, a motor control device, particularly a clock controller, is used to activate the electric motor. The clock controller is activated, for example as prescribed by a closed-loop or open-loop control device of an internal combustion engine, in such a way that the electric motor of the fan is operated in a specific clock ratio. This allows virtually any desired activation of the electric motor in its entire power range. Electric motors have tolerances, which are problematic when designing a device, for example the engine cooling system or the air conditioning system, since it is only with difficulty that allowance can be made for them. The tolerances may, for example, concern power consumption, power output and/or efficiency of the motors. If these tolerances are to be restricted, for example by high-precision production and/or rejecting motors that lie outside a tolerance range, comparatively high costs are incurred. Therefore, for reasons of cost, a relatively great tolerance is usually accepted with respect to the electrical power consumption, power output and/or efficiency of electric motors. Allowance must be made for this when designing the device. This means that, with the electric motor that has the lowest power output, a required minimum power, for example air flow rate, must be achieved in the device. The electric motor with the greatest power output in this case produces excess power, for example in the sense of an excess of air, but must similarly still be able to be used. Therefore, the electric motor with the lowest power output is determinative for the design of the power that is output. The requirements must, however, be satisfied by all the electric motors in the authorized tolerance range. This requires that wearing parts of the electric motor, for example the carbon brushes, are designed for the electric motor with the greatest power output, since the greatest effects of wear occur in the case of this motor under full load. Since the design is made to suit the motor with the greatest power output, it is overdimensioned for most intended uses.